1. Field of the Invention
The present invention relates to wireless communications, and specifically to improved power control and thus increased capacity for a Code Division Multiple Access (CDMA) channel using discontinuous transmission, such as a dedicated control channel (DCCH) or supplemental channel (SCH).
2. Description of Related Art
In current code division multiple access (CDMA) communications protocols, a dedicated control channel (DCCH) link is used primarily for data services communications such as file downloads/uploads, Internet access, and email functions. The DCCH channels and supplemental channels (SCHs) employ Discontinuous Transmission (DTX) technology or methodology whereby a transmitter is enabled and frames are transmitted over the air interface when there is information to send and the transmitter is turned off or disabled when there is no information to send. In a CDMA system, channel capacity, or in other words the number of calls that can be supported via the CDMA air interface, is inversely proportional to the collective transmitted power used by all transmitters, such as constituent subscriber devices. Thus, to maximize the number of active calls, it is important that each of the subscriber devices maintain a minimum transmission power level that is just suitable for maintaining adequate call or link quality.
To aid in maintaining such a minimum transmission power level and adequate call quality, a CDMA reverse DCCH link outer loop power control algorithm is typically implemented at, for example, a mobile switching office of a wireless service provider. The power control algorithm uses, along with other parameters, the determination of whether a transmitted DCCH frame is good, was erased or was never transmitted (DTXd) to control the outer loop threshold (OLT), which is a dynamic parameter that drives the reverse link power (e.g. subscriber transmitter power level) of the DCCH.
More specifically, upon reception of a good frame, the above power control algorithm adjusts the OLT as follows: OLT(N)=OLT(N−1) (RPC_Step_Down*Step_Down_Factor). In the above calculation, RPC_Step_Down is typically a fixed power value, and Step_Down_Factor is a function of the reverse frame erasure rate (FER) target and actual FER.
Upon reception of an erased frame, the above power control algorithm adjusts the OLT as follows: OLT(N)=OLT(N−1)+(RPC_Step_Up*Step_Up_Factor). In this calculation, RPC_Step_Up is typically a fixed power value, and Step_Up_Factor is a function of the reverse frame erase rate (FER) target and actual reverse FER.
Upon reception of a DTXd frame, a frame that was never transmitted, the power control algorithm does not make an adjustment. Thus for proper or accurate power control it is important to distinguish between an erased frame, namely one that could not be decoded or properly received due to channel induced errors, and a DTXd frame
A DCCH rate determination algorithm (RDA), which is typically programmed into a service provider base transceiver station (BTS), actually makes the determination of whether a frame is good, erased or DTXd, and it relies on information similar to that relied on by a fundamental channel (FCH) multi-rate determination algorithm, such as cyclic redundancy checking (CRC) verification, symbol error rates and quality metrics. Although misdetermined frames on the FCH result in problems such as diminishment of audio quality and RLP (radio link protocol) aborts, they occur typically very infrequently and therefore do not significantly impact FCH power control.
However, the probability of a misdetermined frame on a DCCH is much greater due to the nature of discontinuous transmission frames and other limitations and shortcomings. This negatively impacts reverse link capacity, as the OLT and thus reverse channel average power is often increased when in fact it should be maintained at its current level. A similar negative impact occurs for frame misdeterminations on, for example, an IS-2000 supplemental channel (SCH).
Therefore, what is needed is a method and apparatus for improving power control performance and thus increasing channel capacity for a DCCH or SCH in a CDMA system.